Isocyanate-Based Prepolymer

ABSTRACT

The invention relates to an isocyanate-containing prepolymer obtainable by reacting at least one isocyanate which comprises methylene diphenyl diisocyanate with at least one first compound selected from the group comprising monohydric alcohols, thiols and secondary amines and with at least one second compound selected from the group comprising monohydric alcohols, thiols and secondary amines.

FIELD OF THE INVENTION

The present invention relates to isocyanate-based prepolymers and usesthereof.

BACKGROUND TO THE INVENTION

Prepolymers bearing isocyanate groups are commonly used in industry tomake a wide variety of polyurethane products. These prepolymers areusually prepared by mixing a polyol with an excess of a monomericpolyisocyanate, for example, a diisocyanate such as methylene diphenyldiisocyanate (MDI). Disadvantages associated with the process forforming these prepolymers, involve the unreacted monomers.

In the art, several methods exist to reduce free monomer content inprepolymers. Monomers can be stripped by distillation, more inparticular for higher vapor pressure diisocyanate based prepolymers.Methylene diphenyl diisocyanates, on the other hand, have very low vaporpressures. Furthermore, vapor pressure is proportional to concentration.This combination makes it extremely difficult to remove methylenediphenyl diisocyanate monomers from prepolymers down to extremely lowlevels. In addition, the temperature during distillation is preferablynot raised above 220° C., since MDI may start to form carbodiimides andCO₂. This process is expensive, requires high cost equipment, and a highinvestment for low vacuum pumps.

Alternatively, free monomer content can be reduced by asymmetricprepolymerization. However, as a result, the reactivity and curingbehavior with water can be extremely low due to the full 2,4-isomercontent. The mechanical properties for such prepolymers are lessdesirable as well. Additionally, raw material availability and price maybe an issue.

Therefore, there remains a need for prepolymers and processes to preparesaid prepolymers that overcome one or more of the aforementioned issues.It is an object of the present invention to overcome one or more of theaforementioned issues. More in particular, it is an object of thepresent invention to reduce free monomer content in prepolymers. More inparticular, it is an object of the present invention to reduce freemonomer content in prepolymers, while keeping good processability thanksto low viscosity. More in particular, it is an object of the presentinvention to reduce free monomer content in prepolymers, while keepinggood mechanical properties. More in particular, it is an object of thepresent invention to reduce free monomer content in prepolymers, whilekeeping good processability thanks to low viscosity and good mechanicalproperties.

SUMMARY OF THE INVENTION

The present inventors have now surprisingly found that one or more ofthese objects can be obtained by reacting at least one isocyanate withat least two compounds each different and independently selected fromthe group comprising monohydric alcohol, thiol and secondary amine.

According to a first aspect of the present invention, anisocyanate-containing prepolymer is provided, said prepolymer beingobtainable by reacting at least one isocyanate with at least one firstcompound and with at least one second compound different from said atleast one first compound, both compounds being each independentlyselected from the group comprising monohydric alcohols, thiols andsecondary amines; and wherein the at least one isocyanate comprises amethylene diphenyl diisocyanate.

According to a second aspect, the present invention also encompasses aprocess for preparing an isocyanate-containing prepolymer according tothe first aspect, comprising the steps of:

(a) reacting at least one isocyanate with at least one first compoundselected from the group comprising monohydric alcohols, thiols andsecondary amines; and(b) reacting the at least one isocyanate and/or the product of step (a)with at least one second compound selected from the group comprisingmonohydric alcohols, thiols and secondary amines, wherein said secondcompound is different from said first compound;thereby preparing an isocyanate-containing prepolymer.

According to a third aspect, the invention encompasses a polyisocyanatecomposition comprising the isocyanate-containing prepolymer according tothe first aspect of the invention.

According to a fourth aspect, the present invention also encompasses theuse of the prepolymer according to the first aspect of the invention, orthe use of the polyisocyanate composition according to the third aspectof the invention, as a one component adhesive or as a component in a twocomponent adhesive, preferably wherein the adhesive is a hot meltadhesive or a laminating adhesive.

According to a fifth aspect, the invention encompasses an adhesivecomprising the prepolymer according to the first aspect of theinvention, or the polyisocyanate composition according to the thirdaspect of the invention.

According to a sixth aspect, the invention encompasses a one componentself leveling liquid membrane prepared from a prepolymer according tothe first aspect of the invention, or from a polyisocyanate compositionaccording to the third aspect of the invention.

The independent and dependent claims set out particular and preferredfeatures of the invention. Features from the dependent claims may becombined with features of the independent or other dependent claims asappropriate.

The above and other characteristics, features and advantages of thepresent invention will become apparent from the following detaileddescription, which illustrates, by way of example, the principles of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Before the present formulations of the invention are described, it is tobe understood that this invention is not limited to particularformulations described, since such formulations may, of course, vary. Itis also to be understood that the terminology used herein is notintended to be limiting, since the scope of the present invention willbe limited only by the appended claims.

As used herein, the singular forms “a”, “an”, and “the” include bothsingular and plural referents unless the context clearly dictatesotherwise. By way of example, “an isocyanate group” means one isocyanategroup or more than one isocyanate groups.

The terms “comprising”, “comprises” and “comprised of” as used hereinare synonymous with “including”, “includes” or “containing”, “contains”,and are inclusive or open-ended and do not exclude additional,non-recited members, elements or method steps. It will be appreciatedthat the terms “comprising”, “comprises” and “comprised of” as usedherein comprise the terms “consisting of”, “consists” and “consists of”.

Throughout this application, the term “about” is used to indicate that avalue includes the standard deviation of error for the device or methodbeing employed to determine the value.

As used herein, the terms “% by weight”, “wt %”, “weight percentage”, or“percentage by weight” are used interchangeably.

The recitation of numerical ranges by endpoints includes all integernumbers and, where appropriate, fractions subsumed within that range(e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, anumber of elements, and can also include 1.5, 2, 2.75 and 3.80, whenreferring to, for example, measurements). The recitation of end pointsalso includes the end point values themselves (e.g. from 1.0 to 5.0includes both 1.0 and 5.0). Any numerical range recited herein isintended to include all sub-ranges subsumed therein.

All references cited in the present specification are herebyincorporated by reference in their entirety. In particular, theteachings of all references herein specifically referred to areincorporated by reference.

Unless otherwise defined, all terms used in disclosing the invention,including technical and scientific terms, have the meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. By means of further guidance, term definitions are included tobetter appreciate the teaching of the present invention.

In the following passages, different aspects of the invention aredefined in more detail. Each aspect so defined may be combined with anyother aspect or aspects unless clearly indicated to the contrary. Inparticular, any feature indicated as being preferred or advantageous maybe combined with any other feature or features indicated as beingpreferred or advantageous.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, appearances of the phrases“in one embodiment” or “in an embodiment” in various places throughoutthis specification are not necessarily all referring to the sameembodiment, but may. Furthermore, the particular features, structures orcharacteristics may be combined in any suitable manner, as would beapparent to a person skilled in the art from this disclosure, in one ormore embodiments. Furthermore, while some embodiments described hereininclude some but not other features included in other embodiments,combinations of features of different embodiments are meant to be withinthe scope of the invention, and form different embodiments, as would beunderstood by those in the art. For example, in the appended claims, anyof the claimed embodiments can be used in any combination.

According to a first aspect of the present invention, anisocyanate-containing prepolymer is provided, said prepolymer beingobtainable by reacting at least one isocyanate with at least one firstcompound selected from the group comprising monohydric alcohols, thiolsand secondary amines; and with at least one second compound selectedfrom the group comprising monohydric alcohols, thiols and secondaryamines; wherein said first and second compounds are different; andwherein the at least one isocyanate comprises a methylene diphenyldiisocyanate. Said prepolymer can also be obtainable by mixing at leastone isocyanate with at least one first compound selected from the groupcomprising monohydric alcohols, thiols and secondary amines; and with atleast one second compound selected from the group comprising monohydricalcohols, thiols and secondary amines; wherein said first and secondcompounds are different; and wherein the at least one isocyanatecomprises a methylene diphenyl diisocyanate.

Preferably, the prepolymer is obtainable from a stepwise mixing and/orreacting with a first compound and a second compound. In a preferredembodiment, said prepolymer is obtainable by mixing and/or reacting atleast one isocyanate with at least one first compound selected from thegroup comprising monohydric alcohols, thiols and secondary amines; andsubsequently with at least one second compound selected from the groupcomprising monohydric alcohols, thiols and secondary amines; whereinsaid first and second compounds are different; and wherein the at leastone isocyanate comprises a methylene diphenyl diisocyanate.

In some embodiments, the at least one isocyanate is mixed and/or reactedwith two or more compounds selected from the group comprising monohydricalcohols, thiols and secondary amines.

As used herein, the term “isocyanate-containing prepolymer” refers to aprepolymer comprising at least one isocyanate —N═C═O group, whereby theisocyanate group may be a terminating group. Preferably, the isocyanategroup is a terminating group.

The prepolymer according to the first aspect of the invention isprepared from at least one isocyanate, wherein the at least oneisocyanate comprises a methylene diphenyl diisocyanate.

In a preferred embodiment, the methylene diphenyl diisocyanate has afunctionality of at least 2.0, preferably at least 2.2, more preferablyat least 2.4, more preferably at least 2.6, more preferably at least2.8. As used herein, the term “functionality” refers to the averagenumber of isocyanate groups per molecule, averaged over a statisticallyrelevant number of molecules present in the isocyanate.

In another preferred embodiment, the at least one isocyanate comprisespolymeric methylene diphenyl diisocyanate. This can be any mixture ofpure MDI (2,4′-, 2,2′- and 4,4′-methylene diphenyl diisocyanate) andhigher homologues of formula (I):

wherein n is an integer which can be from 1 to 10, preferably from 1 to5.

In an embodiment, the at least one isocyanate is present in an amount ofat least 15% by weight, preferably at least 20% by weight, preferably atleast 25% by weight, preferably at least 30% by weight based on thetotal weight of the prepolymer.

The at least one isocyanate may also comprise another polyisocyanate.Preferably this polyisocyanate comprises a high functionalitypolyisocyanate, with a functionality of at least 2.8, preferably atleast 2.9, preferably at least 3.0. Non-limiting examples ofpolyisocyanates which may be used in the prepolymer of the presentinvention include aliphatic isocyanates such as hexamethylenediisocyanate; m- and p-phenylene diisocyanate, tolylene-2,4- andtolylene-2,6-diisocyanate (also known as toluene diisocyanate, andreferred to as TDI, such as 2,4-TDI and 2,6-TDI) in any suitable isomermixture, chlorophenylene-2,4-diisocyanate, naphthylene-1,5-diisocyanate,diphenylene-4,4′-diisocyanate, 4,4′-diisocyanate-3,3′-dimethyl-diphenyl,3-methyl-diphenylmethane-4,4′-diisocyanate and diphenyl etherdiisocyanate; and cycloaliphatic diisocyanates such as cyclohexane-2,4-and -2,3-diisocyanate, 1-methylcyclohexyl-2,4- and -2,6-diisocyanate andmixtures thereof and bis-(isocyanatocyclohexyl)methane (e.g.4,4′-diisocyanatodicyclohexylmethane (H12MDI)), triisocyanates such as2,4,6-triisocyanatotoluene and 2,4,4-triisocyanatodiphenylether,isophorone diisocyanate (IPDI), butylene diisocyanate,trimethylhexamethylene diisocyanate, isocyanatomethyl-1,8-octanediisocyanate, tetramethylxylene diisocyanate (TMXDI),1,4-cyclohexanediisocyanate (CDI), and tolidine diisocyanate (TODI).

According to the first aspect of the present invention, theisocyanate-containing prepolymer is obtainable by reacting the at leastone isocyanate with at least one first compound and a second compounddifferent from said first compound, each of said first and secondcompound being independently selected from the group comprisingmonohydric alcohols, thiols and secondary amines.

Preferably, the first compound is a monohydric alcohol. Preferably, thesecond compound is a monohydric alcohol different from said firstcompound. Preferably, the first compound and the second compound are twomonohydric alcohols.

As used herein, the terms “monohydric alcohol”, “mono-alcohol”,“mono-ol”, or “monol” are synonymous and used interchangeably and referto an alcohol containing one and only one (1) free hydroxyl (—OH) group.

Non-limiting examples of suitable monohydric alcohols comprise C₁₋₂₀linear, branched or cyclic hydroxyalkyl containing only one free OHgroup (also referred as monohydric C₁₋₂₀ hydroxyalkyl); polyesterscontaining only one free OH group (monohydric polyester), heterocyclylcontaining only one free OH group (monohydric heterocyclyl); oxygencontaining heterocyclyl containing only one free OH group, and blendsthereof. For example, said monohydric alcohol can be a C₁₋₂₀ monohydrichydroxyalkyl, a C₂₋₁₈ monohydric hydroxyalkyl, C₃₋₁₈ monohydrichydroxyalkyl, a C₄₋₁₈ monohydric hydroxyalkyl, a C₅₋₁₈ monohydrichydroxyalkyl, a C₆₋₁₈ monohydric hydroxyalkyl, or a C₆₋₁₈ monohydrichydroxyalkyl. Suitable polyesters comprise compounds containing at leastone ester group and bearing at least one pendant alkyl or alkenyl groupof at least four carbon atoms, said alkyl or said alkenyl group beingsubstituted with only one free hydroxyl group. Examples of suitablemonohydric oxygen containing heterocyclyl are cyclic trimethylolpropaneformal and trimethylolpropane oxetane.

In some embodiments, the first compound is a monohydric alcohol selectedfrom the group comprising monohydric polyesters, monohydric C₁₋₂₀hydroxyalkyl, and monohydric heterocyclyl. In some embodiments, thefirst compound can be a polyester containing only one free OH group,preferably a polyester polyol containing only one free OH group.

In some embodiments, the second compound is a monohydric alcoholselected from the group comprising: monohydric C₁₋₂₀ hydroxyalkyl,monohydric polyesters, and monohydric heterocyclyl. Preferably, thesecond compound is a C₁₀₋₂₀ hydroxyalkyl or blends thereof.

In some embodiments, the first compound can be a monohydric polyester;and the second compound can be selected from monohydric C₄₋₂₀hydroxyalkyl or blends thereof, or monohydric heterocyclyls. Preferably,the first compound can be a monohydric polyester; and the secondcompound can be selected from monohydric C₄₋₂₀ hydroxyalkyl or blendsthereof.

In some embodiment, the first compound can be a monohydric polyester andthe second compound can be a blend of C₁₂-C₁₃ primary alcohols.

The term “alkyl” as a group or part of a group as used herein refers tobranched or straight (linear) or cyclic hydrocarbon with no site ofunsaturation, preferably having at least 4 carbon atoms in the chain.When a subscript is used herein following a carbon atom, the subscriptrefers to the number of carbon atoms that the named group may contain.Thus, for example, C₁₋₂₀ alkyl means an alkyl of 1 to 20 carbon atoms.

The term “hydroxyalkyl” and “monohydric hydroxyalkyl” as used hereinrefers to an alkyl group, as defined above, being substituted with onehydroxyl (—OH) substituent.

The term “alkenyl” as a group or part of a group as used herein refersto a branched or straight or cyclic hydrocarbon with at least one site(usually 1 to 3, preferably 1) of unsaturation, namely a carbon-carbon,sp2 double bond, preferably having at least 4 carbon atoms in the chain.The double bond may be in the cis or trans configuration.

In some embodiments, the first compound is a monohydric alcohol having aweight average molecular weight ranging from 32 to 20 000 Da.Preferably, the first compound is a monohydric alcohol having a weightaverage molecular weight ranging from 100 to 15 000 Da, for example from500 to 10 000 Da, preferably from 800 to 10 000 Da.

In some embodiments, the second compound is a monohydric alcohol havinga weight average molecular weight ranging from 32 to 20 000 Da.Preferably, the second compound is a monohydric alcohol having a weightaverage molecular weight ranging from 50 to 15 000 Da, preferably from100 to 10 000 Da.

In some embodiments, the two or more compounds are monohydric alcoholshaving a weight average molecular weight ranging from 32 to 20 000 Da.Preferably, the two or more compounds are monohydric alcohols wherein afirst monohydric alcohol has a weight average molecular weight rangingfrom 100 to 15 000 Da, preferably from 800 to 10 000 Da and a secondmonohydric alcohol has a weight average molecular weight ranging from 50to 15 000 Da, preferably ranging from 100 to 10 000 Da, more preferablyranging from 100 to 800 Da, more preferably ranging from 100 to 500 Da,yet more preferably ranging from 100 to 300 Da.

In an embodiment, the prepolymer is prepared by first reacting at leastone isocyanate with at least one first monohydric alcohol having aweight average molecular weight ranging from 800 to 10 000 Da, andsubsequently adding to the reaction mixture at least one secondmonohydric alcohol having a lower weight average molecular weight thansaid first monohydric alcohol. In a preferred embodiment, the prepolymeris prepared by first reacting at least one isocyanate with at least onefirst monohydric alcohol having a weight average molecular weightranging from 800 to 10 000 Da, and subsequently adding to the reactionmixture at least one second monohydric alcohol having a weight averagemolecular weight ranging from 100 to 800 Da. Preferably, the firstmonohydric alcohol is a monohydric polyester; and the second monohydricalcohol is selected from monohydric C₄₋₂₀ hydroxyalkyl or blendsthereof, or monohydric heterocyclyls.

In an embodiment, the first compound is a thiol. In an embodiment, thesecond compound is a thiol. In an embodiment, the first and secondcompounds are thiols. As used herein, the term “thiol” refers tocompounds comprising at least one free sulfhydryl (—SH) group,preferably one sulfhydryl group. Suitable thiol can be selected fromC₁₋₁₅ linear or branched thioalkyl, preferably C₂₋₅ linear or branchedthioalkyl, or polyesters substituted with one or more thiol groups.Suitable polyesters comprise compounds containing at least one estergroup and bearing at least one pendant alkyl or alkenyl group of atleast four carbon atoms, said alkyl or said alkenyl group beingsubstituted with at least one thiol group. Suitable thiols can beselected from the group comprising ethanethiol (e-mercaptan),butanethiol (n-butyl mercaptan), tert-butyl mercaptan, and pentanethiols(pentyl mercaptan), such as 1-pentanethiol.

In an embodiment, the first compound is a secondary amine. In anembodiment, the second compound is a secondary amine. In an embodiment,the first and second compounds are a secondary amine. As used herein,the term “secondary amine” refers to a compound comprising at least onesecondary amine group, preferably comprising one and only one (1)secondary amine group. A non-limiting example of a suitable amine isN,N,N′,N′-tetramethyldipropylenetriamine (also known as Jeffcat Z-130,commercially available from Huntsman).

In some embodiments, said at least one first compound and said at leastone second compound are present in a total amount of at least 40% byweight based on the total weight of the isocyanate-containingprepolymer.

Said first compound and said second compound can be present in a totalamount of at least 40% by weight based on the total weight of theprepolymer; preferably in an amount of at least 45% by weight,preferably in an amount of at least 50% by weight, preferably in anamount of at least 55% by weight, preferably in an amount of at least60% by weight, preferably in an amount of at least 65% by weight,preferably in an amount of at least 70% by weight, preferably in anamount of at least 75% by weight, preferably in an amount of at least80% by weight. In some embodiments, said first compound and said secondcompound can be present in a total amount of at least 40% to at most 90%by weight based on the total weight of the prepolymer, preferably in anamount of at least 50% to at most 90%, preferably in an amount of atleast 60% to at most 90%, preferably in an amount of at least 70% to atmost 90%, preferably in an amount of at least 80% to at most 87%.

In an embodiment, said first compound and said second compound aremonohydric alcohols, and are present in a total amount of at least 40%by weight based on the total weight of the prepolymer; preferably in anamount of at least 45% by weight, preferably in an amount of at least50% by weight, preferably in an amount of at least 55% by weight,preferably in an amount of at least 60% by weight, preferably in anamount of at least 65% by weight, preferably in an amount of at least70% by weight, preferably in an amount of at least 75% by weight. Insome embodiments, said monohydric alcohols can be present in a totalamount of at least 40% to at most 90% by weight based on the totalweight of the prepolymer, preferably in an amount of at least 50% to atmost 90%.

In a preferred embodiment, the at least one first compound is present ina total amount of at least 40% by weight based on the total weight ofthe isocyanate-containing prepolymer; preferably in an amount of atleast 45% by weight, preferably in an amount of at least 50% by weight,preferably in an amount of at least 55% by weight, preferably in anamount of at least 60% by weight. In some embodiments, said firstcompound can be present in a total amount of at least 40% to at most 90%by weight based on the total weight of the prepolymer, preferably in anamount of at least 50% to at most 80%, preferably in an amount of atleast 60% to at most 70%.

In an embodiment, said first compound is a monohydric alcohol, and ispresent in a total amount of at least 40% by weight based on the totalweight of the prepolymer; preferably in an amount of at least 45% byweight, preferably in an amount of at least 50% by weight, preferably inan amount of at least 55% by weight, preferably in an amount of at least60% by weight. In some embodiments, said monohydric alcohol can bepresent in a total amount of at least 40% to at most 90% by weight basedon the total weight of the prepolymer, preferably in an amount of atleast 50% to at most 80%.

In a preferred embodiment, said second compound is present in an amountof at least 0.001% by weight based on the total weight of theprepolymer; preferably in an amount of at least 0.010% by weight; forexample in an amount of at least 0.100% by weight, for example at least1.0% by weight, for example 5.0% by weight based on the total weight ofthe prepolymer. In some embodiments, said second compound is present inat most 50.0% by weight, preferably in at most 30.0% by weight,preferably in at most 20.0% by weight, based on the total weight of theprepolymer. In a preferred embodiment, said second compound is amonohydric alcohol, and is present in an amount of at least 0.001% byweight, for example in an amount of at least 0.010% by weight, forexample in an amount of at least 0.100% by weight based on the totalweight of the prepolymer.

In some embodiments, said second compound is a monohydric alcoholcomprising at least one tertiary amine group, and is present in anamount of at least 0.001% by weight based on the total weight of theprepolymer. In an embodiment, said second compound comprises at leastone tertiary amine group and is present in a total amount of at least0.001% and at most 20.0% by weight based on the total weight of theprepolymer. In an embodiment, said second compound is a monohydricalcohol comprising at least one tertiary amine group and is present in atotal amount of at least 0.001% and at most 20.0% by weight based on thetotal weight of the prepolymer.

In some embodiments, said at least one first compound is present in anamount of at least 40% by weight based on the total weight of theprepolymer, preferably at least 50% by weight, and said second compoundis present in an amount of at least 0.001% by weight based on the totalweight of the prepolymer.

In some embodiments, said first and second compounds are monohydricalcohols, and said at least one first monohydric alcohol is present inan amount of at least 40% by weight based on the total weight of theprepolymer, preferably at least 50% by weight, and said secondmonohydric alcohol is present in an amount of at least 0.1% by weightbased on the total weight of the prepolymer.

In some embodiments, said first and second compounds are monohydricalcohols, and can be present in a total amount of at least 40.1% byweight based on the total weight of the prepolymer; preferably at least50.1% by weight, preferably at least 60.1% by weight, and said secondmonohydric alcohol has a lower weight average molecular weight than saidat least one first monohydric alcohol.

In some embodiments, said first and second compounds are monohydricalcohols, said first compound is present in an amount of at least 40% byweight based on the total weight of the prepolymer, said second compoundis present in an amount of at least 0.1% by weight based on the totalweight of the prepolymer and has a lower weight average molecular weightthan said first compound.

In some embodiments, the first compound is a polyester containing onlyone free OH group, preferably a polyester polyol containing only onefree OH group, preferably in an amount of at least 40% by weight basedon the total weight of the prepolymer. In some embodiments, the compoundcan be a monohydric polyester; and the second compound is a monohydricalcohol selected from monohydric C₁₋₂₀ hydroxyalkyl or blends thereof,and monohydric heterocyclyls. For example, the first compound can be amonohydric polyester, and can be present in an amount of at least 40% byweight based on the total weight of the prepolymer; and the secondcompound can be selected from monohydric C₁₋₂₀ hydroxyalkyl or blendsthereof, and monohydric heterocyclyls, and can be present in an amountof at least 0.1% by weight based on the total weight of the prepolymer.

In some embodiments, said second compound has a different weight averagemolecular weight than said at least one first compound. In a preferredembodiment, said second compound has a lower weight average molecularweight than said at least one first compound. In a preferred embodiment,said second compound has a different steric hindrance than said at leastone first compound. This can be obtained for example by using differentbranching structures for the first and second compound.

Preferably, the first compound is a monohydric alcohol, and the secondcompound is a second monohydric alcohol different from the first one.Said first and second monohydric alcohols can have different weightaverage molecular weight M_(w) and/or different OH value. In anembodiment, said second monohydric alcohol has a different weightaverage molecular weight than said at least one first monohydricalcohol. In a preferred embodiment, said second monohydric alcohol has alower weight average molecular weight than said at least one firstmonohydric alcohol. In a preferred embodiment, the first and secondmonohydric alcohols have a different steric hindrance.

In some embodiments said first compound comprises at least one tertiaryamine group. In some embodiment, said second compound comprises at leastone tertiary amine group. For example, said first compound can be amonohydric alcohol which comprises at least one tertiary amine group andsaid second compound can be a monohydric alcohol which comprises atleast one tertiary amine group. For example, said monohydric alcohol canbe a monohydric polyester substituted with at least one tertiary aminegroup, a monohydric C₁₋₂₀ hydroxyalkyl substituted with at least onetertiary amine group, or a monohydric heterocyclyl substituted with atleast one tertiary amine group. Such tertiary amino groups can be usedto increase the blowing and gelling catalytic activity. Preferredcompounds comprising a tertiary amine group may be selected from thegroup comprising: N,N,N′-trimethyl-N′-hydroxyethyl-bisaminoethylether(also known as Jeffcat ZF-10, commercially available from Huntsman),2-(2-dimethylaminoethoxy)ethanol (also known as DMEE or Jeffcat ZR-70,commercially available from Huntsman),N,N,N′-trimethylaminoethyl-ethanolamine (also known as Jeffcat Z-110,commercially available from Huntsman),N,N-bis(3-dimethylaminopropyl)-N-isopropanolamine (also known as JeffcatZR-50, commercially available from Huntsman), andN,N-dimethylethanolamine (also known as DMEA, commercially availablefrom Huntsman).

In a preferred embodiment, the invention provides theisocyanate-containing prepolymer according to the first aspect of theinvention, wherein the ratio of the NCO value of theisocyanate-containing prepolymer, to the weighted average of the OH, SHor NH value, of said first and second monohydric alcohol, thiol orsecondary amine respectively ranges from 0.0005 to 1.0000, preferablyfrom 0.0005 to 0.7500, preferably from 0.0010 to 0.600.

The NCO value (also referred to as percent NCO or NCO content) of theisocyanate-containing prepolymer is preferably measured by titrationwith dibutylamine according to the DIN 53185 standard. The NCO value isexpressed in weight %.

The OH value (also referred to as OH number or OH content) is preferablymeasured according to the ASTM D 1957 standard. The OH value isexpressed in mg KOH/g. The SH value (also referred to as mercapto value)can be measured by titration with KOH. In brief, SH groups areacetylated with acetic anhydride in the presence of a suitable Lewisbase. The excess acetic anhydride is hydrolyzed with water and theresulting acetic acid is titrated with a potassium hydroxide solution.The SH value can then be calculated using the following equation: SHvalue(mg KOH/g)=14.025×(B−A)×N/S wherein S represents a sample weight(g); A represents the amount (mL) of the solution of potassium hydroxiderequired for titrating the sample; B represents the amount (mL) of thesolution of potassium hydroxide required for a blank test; and Nrepresents the normality of the potassium hydroxide solution.

The NH value can be determined by titration of the sample in ethanolsolution with standardized 0.1 N HCl by using bromoresol green solutionas an indicator.

The weighted average can be calculated as follows. If for example thereare 4 parts of a first monol to 3 parts of a second monol, then theweighted average of the OH value is (4×OH value of monol 1+3×OH value ofmonol 2)/(4+3). In those embodiments where the at least one isocyanateis reacted with two or more compounds selected from the group comprisingmonohydric alcohols, thiols and secondary amines, the weighted averageof the OH value can be calculated from the OH values and the relativeconcentrations of said two or more compounds.

When the ratio of the NCO value of the isocyanate-containing prepolymerto the weighted average of the OH, SH or NH value of said first andsecond monohydric alcohol, thiol or secondary amine respectively rangesfrom 0.0005 to 1.0000, preferably from 0.0005 to 0.7500, it rangespreferably from 0.0010 to 0.6000, preferably from 0.0010 to 0.2000,preferably from 0.0010 to 0.1000, preferably from 0.0010 to 0.0500,preferably from 0.0010 to 0.0200, preferably from 0.0020 to 0.0200, forexample from 0.0050 to 0.0200, preferably from 0.0050 to 0.0150.

Preferably the NCO value of the prepolymer is at most 15.0%, preferablyat most 10.0%, preferably at most 5.0%, preferably at most 2.0%.

The present inventors have found that the prepolymer according to thefirst aspect of the invention can have an improved processability, dueto low viscosity. This effect was even observed without the need of aplasticizer.

Preferably, the viscosity is measured before addition of a plasticizeror a viscosity reducer, herein referred to as a “non-plasticizedprepolymer”. In a preferred embodiment, the viscosity of the(non-plasticized) prepolymer ranges from 1000 to 200 000 mPa·s, forexample from 1500 to 150 000 mPa·s, for example from 2000 to 100 000mPa·s, for example from 2500 to 50 000 mPa·s, for example from 5000 to20 000 mPa·s, for example from 5000 to 18 000 mPa·s, for example from5000 to 15 000 mPa·s, wherein the viscosity is measured at 25° C. usingBrookfield Viscometer (model DV-II, spindle 21, rpm according 30-80% offull scale) according to the ASTM D 4889 standard without anyplasticizer added to the prepolymer.

The present inventors have also found that the prepolymer can have areduced content in free isocyanate monomers, such as methylene diphenyldiisocyanate monomers in the form of 2,4′, 2,2′ and 4,4′ isomers andmixtures thereof.

In some embodiments, the prepolymer according to the first aspect of theinvention comprises at most 10.0% by weight of free isocyanate monomers,preferably at most 5.0% by weight of free monomers, preferably at most3.0% by weight of free monomers, preferably at most 2.0% by weight offree monomers, preferably at most 1.0% by weight of free monomers,preferably at most 0.5% by weight of free monomers, most preferably atmost 0.1% by weight of free monomers, with % by weight based on 100% ofthe total weight of the prepolymer. Preferably, the free isocyanatemonomer content is measured before addition of a plasticizer or aviscosity reducer. Preferably, the free isocyanate monomer content ismeasured by quantitative HPLC GC analysis.

The prepolymer may comprise one or more additives. In some embodiments,the additive is present in an amount of at least 0.01% by weight, forexample at least 0.03% by weight, for example at least 0.1% by weight,preferably at least 0.3% by weight, for example at least 0.5%, forexample at least 1.0% by weight, based on the total weight of theprepolymer.

The additive may be a plasticizer. Preferably, the amount of plasticizerin the prepolymer is limited. In a preferred embodiment, the prepolymercomprises from 0.0% to at most 50.0% by weight of plasticizer,preferably from 0.0% to at most 15.0% by weight of plasticizer,preferably from 0.0% to at most 10.0% by weight of plasticizer,preferably from 0.0% to at most 5.0% by weight of plasticizer,preferably from 0.0% to at most 1.0% by weight of plasticizer,preferably from 0.00% to at most 0.01% by weight of plasticizer,preferably from 0.000% to at most 0.001% by weight of plasticizer, basedon the total weight of the prepolymer.

Suitable plasticizers, for purposes of the present invention, compriseconventional plasticizers known in the art, such as esters of dibasic orpolybasic carboxylic acids with monohydric alcohols. Non-limitingexamples of such polycarboxylic acids may be selected from the groupcomprising succinic acid, isophthalic acid, trimellitic acid, phthalicacid anhydride, tetrahydrophthalic acid anhydride, hexahydrophthalicacid anhydride, endomethylene-tetrahydrophthalic acid anhydride,glutaric acid anhydride, maleic acid anhydride, fumaric acid and dimericand trimeric fatty acids (such as oleic acid), and combinations thereof,which may be mixed with monomeric fatty acids. Suitable monohydricalcohols are as described and exemplified above.

Other examples of suitable plasticizers may be selected from the groupcomprising phthalates, such as dioctyl phthalate, diisooctyl phthalate,diisononyl phthalate, dimethyl phthalate, dibutyl phthalate; phosphates,such as tributyl phosphate, triethyl phosphate (TEP), triphenylphosphate and cresyl diphenyl phosphate; chlorinated biphenyls; aromaticoils; adipates, such as diisononyl adipate and di-(2-ethylhexyl)adipate; and combinations thereof. Specific examples of suitableplasticizers are commercially available from the BASF Corporation underthe trademark of PALATINOL®, such as PALATINOL® 711P, and under thetrademark of PLASTOMOLL®, such as PLASTOMOLL® DNA and PLASTOMOLL® DOA.

Other examples of suitable plasticizers, comprise phosphoric acid estersof the above-mentioned branched and unbranched aliphatic, cycloaliphaticand aromatic alcohols. If appropriate, phosphates of halogenatedalcohols, for example, trichloroethyl phosphate, can also be employed.It is to be appreciated that mixed esters of the aforementioned alcoholsand carboxylic acids can also be employed. So called polymericplasticizers can also be employed, for purposes of the presentinvention. Examples of such plasticizers may be selected from the groupcomprising polyesters of adipic acid, sebacic acid or phthalic acid.Phenol alkysulfonates, e.g. phenyl paraffinsulfonates, can also beemployed. It is to be appreciated that the prepolymer may comprise anycombination of two or more of the aforementioned plasticizers.Alternatively, such plasticizers may also be selected from alkylenecarbonates, such as propylene carbonate and ethylene carbonate. Theseare commercially available from Huntsman under the Jeffsol® trademark.

The additive may be an amine. In a preferred embodiment the prepolymercomprises at least one amine. Preferably, the amine is a secondaryamine, for example dibutylamine.

According to a second aspect, the present invention also encompasses aprocess for preparing an isocyanate-containing prepolymer comprising thesteps of:

(a) reacting at least one isocyanate with at least one first compoundselected from the group comprising monohydric alcohols, thiols andsecondary amines; and(b) reacting the at least one isocyanate and/or the product of step (a)with at least one second compound selected from the group comprisingmonohydric alcohols, thiols and secondary amines, wherein said secondcompound is different from said first compound;thereby preparing an isocyanate-containing prepolymer.

Said process can also comprise the steps of:

(a) mixing at least one isocyanate with at least one first compoundselected from the group comprising monohydric alcohols, thiols andsecondary amines; and(b) mixing the at least one isocyanate and/or the product of step (a)with at least one second compound selected from the group comprisingmonohydric alcohols, thiols and secondary amines, wherein said secondcompound is different from said first compound;thereby preparing an isocyanate-containing prepolymer.

Preferably, the addition of the first and second compounds is a stepwiseprocess. In an embodiment, said process comprises the steps of:

(a) mixing and/or reacting at least one isocyanate with at least onefirst compound selected from the group comprising monohydric alcohols,thiols and secondary amines; and(b) subsequently, mixing and/or reacting the product of step (a) with atleast one second compound selected from the group comprising monohydricalcohols, thiols and secondary amines, wherein said second compound isdifferent from said first compound;thereby preparing an isocyanate-containing prepolymer.

In a preferred embodiment, at least one mixing or reacting step isperformed at a temperature of at least 60° C., preferably at least 65°C., preferably at least 70° C., preferably at least 75° C., preferablyat least 80° C. Preferably, all mixing and reacting steps are performedat said temperature.

The compounds, such as the monohydric alcohols, may be gradually addedto the at least one isocyanate, for example step wise, or they may becontinuously added, for example drop by drop. Preferably, the compoundsare added continuously drop by drop. Preferably, the monohydric alcoholsare continuously added drop by drop.

In some embodiments, at least one mixing or reacting step can beperformed in the presence of a catalyst. All mixing and reacting stepscan also be performed in the presence of a catalyst.

Non-limiting examples of suitable catalysts include non graftedcatalysts, such as 2,2′-dimorpholinodiethylether (DMDEE, availablecommercially from Huntsman), and grafted catalysts, such asdimethylethanolamine (DMEA) and 2(2-dimethylaminoethoxy)ethanol (DMEE).Preferably, the catalyst is 2,2′-dimorpholinodiethylether (DMDEE) or2(2-dimethylaminoethoxy)ethanol (DMEE). Preferably, the catalyst is agrafted catalyst.

In some embodiments, the catalyst is an organometallic catalyst. Inthese embodiments, the catalyst comprises an element selected from thegroup comprising tin, iron, lead, bismuth, mercury, titanium, hafnium,zirconium, and combinations thereof. In certain embodiments, thecatalyst comprises a tin catalyst. Suitable tin catalysts, for purposesof the present invention, may be selected from tin(II) salts of organiccarboxylic acids, e.g. tin(II) acetate, tin(II) octoate, tin(II)ethylhexanoate and tin(II) laurate. In an embodiment, the organometalliccatalyst comprises dibutyltin dilaurate, which is a dialkyltin(IV) saltof an organic carboxylic acid. Specific examples of suitableorganometallic catalyst, e.g. dibutyltin dilaurates, for purposes of thepresent invention, are commercially available from Air Products andChemicals, Inc. under the trademark of DABCO®. The organometalliccatalyst can also comprise other dialkyltin(IV) salts of organiccarboxylic acids, such as dibutyltin diacetate, dibutyltin maleate anddioctyltin diacetate.

Non-limiting examples of other suitable catalysts, may be selected fromthe group comprising iron(II) chloride; zinc chloride; lead octoate;tris(dialkylaminoalkyl)-s-hexahydrotriazines includingtris(N,N-dimethylaminopropyl)-s-hexahydrotriazine; tetraalkylammoniumhydroxides including tetramethylammonium hydroxide; alkali metalhydroxides including sodium hydroxide and potassium hydroxide; alkalimetal alkoxides including sodium methoxide and potassium isopropoxide;and alkali metal salts of long-chain fatty acids having from 10 to 20carbon atoms and/or lateral OH groups; triethylamine,N,N,N′,N′-tetramethylethylenediamine, N,N-dimethylaminopropylamine,N,N,N′,N′,N″-pentamethyldipropylenetriamine,tris(dimethylaminopropyl)amine, N,N-dimethylpiperazine,tetramethylimino-bis(propylamine), dimethylbenzylamine, trimethyl amine,triethanolamine, N,N-diethyl ethanolamine, N-methylpyrrolidone,N-methylmorpholine, N-ethylmorpholine, bis(2-dimethylamino-ethyl)ether,N,N-dimethylcyclohexylamine (DMCHA),N,N,N′,N′,N″-pentamethyldiethylenetriamine, 1,2-dimethylimidazole,3-(dimethylamino) propylimidazole;N,N,N-dimethylaminopropylhexahydrotriazine, potassium acetate,N,N,N-trimethyl isopropyl amine formate, and combinations thereof. It isto be appreciated that the catalyst component may include anycombination of two or more of the aforementioned catalysts.

Preferably, the catalyst can be present in an amount of at least 10 ppm,for example at least 0.01% by weight, for example at least 0.20% byweight, with % by weight being based on the total weight of theprepolymer.

According to a third aspect, the invention encompasses a polyisocyanatecomposition comprising the isocyanate-containing prepolymer according tothe first aspect of the invention.

The present invention encompasses the use of the prepolymer according tothe first aspect of the invention or the polyisocyanate compositionaccording to the third aspect of the invention for the preparation of anadhesive, a coating, an elastomer, a foam, or a polyurethane. Theinvention also encompasses said prepared adhesive, coating, elastomer,foam or polyurethane.

The present invention also encompasses the use of the prepolymeraccording to the first aspect of the invention or the use of thepolyisocyanate composition according to the third aspect of theinvention for the preparation of a polyurethane. The invention alsoencompasses said polyurethane.

The invention encompasses the use of the prepolymer in a one-componentsystem, which can be cured by moisture. The invention also encompassessaid one-component system. The invention also encompasses the use of theprepolymer in a two-component system, preferably in a two-componentpolyurethane or a two-component heat curable polyisocyanurate system.The invention also encompasses said two-component system.

According to a fourth aspect, the present invention also encompasses theuse of the prepolymer according to the first aspect of the invention, orthe use of the polyisocyanate composition according to the third aspectof the invention, as a one component adhesive or as a component in a twocomponent adhesive, preferably wherein the adhesive is a hot meltadhesive or a laminating adhesive. The invention also encompasses saidone component adhesive or said two component adhesive. Preferably theseadhesives are used for laminating an object.

According to a fifth aspect, the invention encompasses an adhesivecomprising the prepolymer according to the first aspect of theinvention, or the polyisocyanate composition according to the thirdaspect of the invention.

The prepolymers according to the invention or the polyisocyanatesobtained therewith are particularly useful as raw material forformulating a one-component (1C), for example moisture curing, adhesive,with free monomer content of at most 1.0 weight %, preferably at most0.5 weight %, preferably at most 0.2 weight %, most preferably at most0.1 weight %. The prepolymers according to the invention or thepolyisocyanates obtained therewith are also particularly useful forformulating a two-component (2C) adhesive, with free monomer content ofat most 1.0 weight %, preferably at most 0.5 weight %, preferably atmost 0.2 weight %, most preferably at most 0.1 weight %.

A one-component adhesive may comprise DIY (do-it-yourself) adhesives,which react with moisture in the air. A two-component system may reactwith a polyol. Preferably, the adhesive is a D4 adhesive. As usedherein, the term D4 adhesive refers to adhesives corresponding to the EN204 specifications for the D4 class. In some embodiments of theinvention, the prepolymer fulfills the D4 (EN 204) specifications forDIY wood adhesives, while showing a free monomer content of at most 1.0weight %, preferably at most 0.5 weight %, preferably at most 0.2 weight%, most preferably at most 0.1 weight %.

Preferably, the adhesive is a hot melt adhesive. The invention alsoencompasses said hot melt adhesive. The prepolymers according to theinvention or the polyisocyanates obtained therewith are particularlyuseful for formulating a reactive hot melt (RHM) adhesive, with freemonomer content of at most 1.0 weight %, preferably at most 0.5 weight%, preferably at most 0.2 weight %, most preferably at most 0.1 weight%.

Preferably, the adhesive is a laminating adhesive. The invention alsoencompasses said laminating adhesive. The prepolymers according to theinvention or the polyisocyanates obtained therewith are particularlyuseful for formulating a laminating adhesive, with free monomer contentof at most 1.0 weight %, preferably at most 0.5 weight %, preferably atmost 0.2 weight %, most preferably at most 0.1 weight %.

In some embodiments, the prepolymer can be particularly useful forformulating a laminating adhesive, and preferably for flexible packagingadhesive. The prepolymers are particularly useful as raw material forformulating fast curing and low migration 1C and 2C flexible packagingadhesives.

Preferably, the laminating adhesive is a 2C system. Some adhesivesaccording to embodiments of the present invention provide bonds suitableto be used in flexible packaging for indirect food contact, due to areduced migration of aromatic amines, i.e. a migration rate below thelegally required limit, for example below a content of 2 ppb ofpolyaromatic amine.

The prepolymer is particularly useful for flexible packaging where alaminated film or sheet, produced using an adhesive, is used.

As an applicator of an adhesive according to the present invention therecan be mentioned known applicators such as airless spray machine, airspray machine, immersion, roll coater, brush and the like. Theconditions used for lamination using an adhesive according to theinvention are preferably 20 to 150° C., for example 20 to 100° C., forexample 40 to 150° C., particularly preferably 40 to 100° C.

In producing a laminated film by using the present adhesive, the filmused is not critical. As the film, there can be mentioned a film ofpolyester type such as polyethylene terephthalate or the like; a film ofpolyolefin type such as polyethylene, polypropylene or the like; a filmof polyamide type such as nylon or the like; a metal foil such asaluminum foil, copper foil or the like; an ethylene-vinyl acetatecopolymer or a saponification product thereof; a cellophane; a polyvinylchloride; a polyvinylidene chloride; a polystyrene; a paper; and soforth. There can also be suitably used stretched products thereof andsurface-treated (e.g. corona discharge-treated or surface-coated)products thereof.

The adhesive of the present invention can be suitably used forlamination not only between two film layers but also between three ormore film layers.

The prepolymers according to the invention or the polyisocyanatesobtained therewith are particularly useful as raw material forformulating a one-component moisture curing self leveling liquidmembrane for coating applications. The present invention encompasses aone component self leveling liquid membrane prepared from a prepolymeraccording to the first aspect of the invention, or from a polyisocyanatecomposition according to the third aspect of the invention.

In some embodiments, two-components systems based on these prepolymers,can achieve permanent tack properties. Accordingly, the presentinvention also encompasses pressure sensitive adhesive prepared usingthe prepolymers according to the invention.

In some embodiments, the prepolymer can be useful for formulating anadhesive for a material comprising lignocellulose, herein also referredto as a “lignocellulosic material”.

The present invention also encompasses a substrate comprising aprepolymer according to the invention. The present invention alsoencompasses a lignocellulosic body prepared using the prepolymeraccording to the invention.

The invention also encompasses the use of the prepolymer for thepreparation of a coating, an elastomer, a one component foam, or a twocomponent foam.

The invention is illustrated but not limited by the following examples.

EXAMPLES

The examples described hereunder illustrate the properties of theprepolymers and compositions according to embodiments of the presentinvention. Unless otherwise indicated, all parts and all percentages inthe following examples, as well as throughout the specification, areparts by weight or percentages by weight respectively.

The following ingredients were used in the preparation of theprepolymers:

Isocyanate 1: polymeric methylene diphenyl isocyanate (pMDI), with anNCO value of 31.0%, with a functionality of 2.7 (softblock content0.0%).Isocyanate 2: polymeric methylene diphenyl isocyanate (pMDI) of NCOvalue 30.5%, with a functionality of 2.85 (softblock content 0.0%).Monol 1: polyester monol of M_(w) 900, and a functionality of 1, basedon transesterification and dehydration reaction products of castor oilwith glycerol.Monol 2: blend of C₁₂-C₁₃ primary alcohols of M_(w) 193, and afunctionality of 1, CAS no 67762-41-8, available as Neodol 23E fromShell Chemicals.Monol 3: CTPF (cyclic trimethylol propane formal) also known as5-ethyl-1,3-dioxane-5-methanol, CAS no 5187-23-5 with M_(w) 146.Monol 4: TMPO (trimethylol propane oxetane) also known as3-ethyl-3-oxetanemethanol, CAS no 3047-32-3 with M_(w) 116.Diol 1: polypropylene glycol of molecular weight 2000 (PPG2000).Diol 2: polypropylene glycol of functionality 2 and molecular weight of125.Secondary amine 1: N,N,N′,N′-tetramethyldipropylenetriamine,commercially available from Huntsman as Jeffcat Z-130.DMDEE: 2,2′-dimorpholinodiethylether.

DMEA: N,N-dimethylethanolamine. Methods

The following methods were used in the examples:

The NCO value (or percent NCO), given in weight %, was measuredaccording to the DIN 53185 standard. In brief, isocyanate is reactedwith an excess of di-n-butylamine to form ureas. The unreacted amine isthen titrated with standard nitric acid to the color change ofbromocresol green indicator or to a potentiometric endpoint. The percentNCO or NCO-value is defined as the percent by weight of NCO-groupspresent in the product.

The OH value (also referred to as OH number or OH content) was measuredaccording to the ASTM D 1957 standard. In brief, hydroxyl groups areacetylated with acetic anhydride in the presence of pyridine and heat.The excess acetic anhydride is hydrolyzed with water and the resultingacetic acid is titrated with standard potassium hydroxide solution. TheOH value is expressed in mg KOH/g sample. The OH value was calculatedusing the following equation:

OH value(mg KOH/g)=56.1×(B−A)×N/S wherein S represents a sample weight(g); A represents the amount (mL) of the solution of potassium hydroxiderequired for titrating the sample; B represents the amount (mL) of thesolution of potassium hydroxide required for a blank test; and Nrepresents the normality of the potassium hydroxide solution.

The concentration in free monomer was measured by quantitative HPLC GCanalysis.

Final lap shear strength in climate condition (after 7 days at 23° C.50% RH), after boiling (a boiling test of 6 hr and after this condition2 hr cold water) and after water immersion (4 days in water at 20°C.+/−5° C.) of prepolymers was determined according to Standard EN204-205.

Example 1

The prepolymers 1-4 were prepared by reacting monol 1, having an OHvalue of 62, with isocyanate 2, and subsequently mixing the product withmonol 2, having an OH value of 290. The formulations are listed in Table1.

The comparative prepolymers 1-4 were obtained by mixing diol 1 having anOH value of 56, with isocyanate 2, and mixing the product with diol 2,having an OH value of 897. The formulations are listed in Table 1.

The comparative prepolymers 1′-4′ were obtained by mixing monol 1,having an OH value of 62, with isocyanate 2. The formulations are listedin Table 1.

The NCO value and the free monomer content of the prepolymers (prepo)were measured. The ratio NCO value of the prepolymer to the weighted OHvalue of the monols or diols (NCO prepo/OH alcohol(s)) was determined.The results are listed in Table 1.

FIG. 1 represents the free monomer content of the prepolymer vis-a-visthe NCO of the prepolymer for the various prepolymers above made eitherwith two diols, two monols or one monol.

It is clear that by using two monols the free monomer content of theprepolymer is decreased compared to using only one monol or using twodiols, especially at low NCO value.

TABLE 1 NCO value NCO Free in prepo/ isocyante Isocyanate 2 Monol 1Monol 2 Diol 1 Diol 2 prepo OH monomer (wt %) (wt %) (wt %) (wt %) (wt%) (wt %) alcohol(s) (wt %) Prepo 1 59.80 32.16 8.04 0.00 0.00 15 0.134910.9 Comp. prepo 1 67.22 0.00 0.00 26.22 6.56 15 0.0669 17.5 Comp. prepo1′ 55.89 44.11 0.00 0.00 0.00 15 0.2419 17.9 Prepo 2 46.83 42.54 10.630.00 0.00 10 0.0929 6.1 Comp. prepo 2 56.65 0.00 0.00 34.68 8.67 100.0446 11.3 Comp. prepo 2′ 41.66 58.34 0.00 0.00 0.00 10 0.1613 10 Prepo3 33.86 52.91 13.23 0.00 0.00 5 0.04645 1.3 Comp. prepo 3 46.07 0.000.00 43.13 10.79 5 0.0223 5.9 Comp. prepo 3′ 27.44 72.56 0.00 0.00 0.005 0.0806 2.1 Prepo 4 23.49 61.21 15.30 0.00 0.00 1 0.0093 <0.1 Comp.prepo 4 37.61 0.00 0.00 49.91 12.48 1 0.0045 1.4 Comp. prepo 4′ 15.0085.00 0.00 0.00 0.00 1 0.0161 0.05

Example 2

The prepolymers 5 and 6, have the same ingredients as prepolymer 3 ofexample 1, but were prepared differently. The prepolymer 3 was preparedby adding monol 1 to isocyanate 2, and then subsequently adding monol 2to the reaction mixture. The prepolymer 5 was prepared by adding monol 2to isocyanate 2, and subsequently adding monol 1 to the reactionmixture. The prepolymer 6 was prepared by simultaneously mixing all theingredients together: isocyanate 2, monol 1 and monol 2. The NCO valueand the free monomer content of the prepolymers was measured andcompared with the free monomer content of prepolymer 3. The formulationsand results are listed in Table 2. The ratio of the NCO value of theprepolymer to the weighted OH value of the monols (NCO prepo/OH) was0.046.

TABLE 2 NCO Free value in Isocyanate First monol Second isocyanate prepo2 added monol added monomer (wt %) = 5 (wt %) (wt %) (wt %) (wt %) Prepo3 33.86 52.91 monol 1 13.23 monol 2 1.3 Prepo 5 33.86 13.23 monol 252.91 monol 1 1.9 Prepo 6 33.86 52.91 monol 1 and 13.23 monol 2 6.2

The prepolymers 7 to 9 have the same ingredients but were prepareddifferently. Prepolymer 7 was prepared by reacting isocyanate 1 withmonol 1 in a first step and subsequently adding monol 3 to the reactionmixture in a second step. Prepolymer 8 was prepared by reactingisocyanate 1 with monol 3 in a first step and subsequently adding monol1 to the reaction mixture in a second step. Prepolymer 9 was prepared bysimultaneously reacting isocyanate 1, with monol 1 and monol 3 in onestep. The formulations are listed in Table 3. The free monomer contentof the prepolymers (prepo) was measured. The results are listed in Table3. The ratio of the NCO value of the prepolymer to the weighted OH valueof the monols (NCO prepo/OH) was 0.039.

TABLE 3 NCO Free value in Isocyanate First monol Second isocyanate prepo1 added monol added monomer (wt %) = 5 (wt %) (wt %) (wt %) (wt %) Prepo7 35.89 51.29 monol 1 12.82 monol 3 0.5 Prepo 8 35.89 12.82 monol 351.29 monol 1 1.2 Prepo 9 35.89 51.29 monol 1 and 12.89 monol 3 2.3

The prepolymers 10 to 12 have the same ingredients but were prepareddifferently. Prepolymer 10 was prepared by reacting isocyanate 2 withmonol 1 in a first step and subsequently adding monol 4 to the reactionmixture in a second step. Prepolymer 11 was prepared by reactingisocyanate 2 with monol 4 in a first step and subsequently adding monol1 to the reaction mixture in a second step. Prepolymer 12 was preparedby simultaneously reacting isocyanate 2, with monol 1 and monol 4 in onestep. The formulations are listed in Table 4. The free monomer contentof the prepolymers (prepo) was measured. The results are listed in Table4. The ratio of the NCO value of the prepolymer to the weighted OH valueof the monols (NCO prepo/OH) was 0.035.

TABLE 4 NCO Free value in Isocyanate First monol Second monol isocyanateprepo 2 added added monomer (wt %) = 5 (wt %) (wt %) (wt %) (wt %) Prepo10 38.30 49.36 monol 1 12.34 monol 4 <0.1 Prepo 11 38.30 12.34 monol 449.36 monol 1 0.4 Prepo 12 38.30 49.36 monol 1 and 12.34 monol 4 0.8

Tables 2-4 also show the effect on the free monomer content of thesteric hindrance of the monol used. Tables 2-4 also show the effect onthe free monomer content of the order in which the monol may be added.

Tables 2-4 also show the effect of the NCO prepo/OH ratio on the freemonomer content of the prepolymer. For example, a small difference inthe ratio NCO prepo/OH between prepolymers 3 and 10 (both with an NCOcontent of 5%), gave a significant difference in free monomer content.

By accurately selecting the monohydric alcohol, the NCO content may beraised, while keeping the free monomer content low. A higher NCO contentof the prepolymer may lead to improved mechanical properties of thecured system.

Example 3

The durability of prepolymers 2, 3, 7 and 10 was further testedaccording to EN-204-205.

After 7 days (final strength) in climate condition (23° C. 50% RH) a lapshear strength was measured. After the final strength was reached, a lapshear strength (water test) was measured after 4 days in water (20+/−5°C.). The final strength also resisted a boiling test of 6 hr and afterthis condition 2 hr cold water. The lap shear measured after the boilingtest is also shown in Table 5.

The prepolymers 2, 3, 7 and 10 achieved the D4 classification.

TABLE 5 Free isocyanate Final strength Boiling Test Water Test monomer(MPa) (MPa) (MPa) (wt %) Prepo 2 12.1 4.8 4.5 6.1 Prepo 3 10.8 4.4 5.11.3 Prepo 7 10.1 4.2 4.8 0.5 Prepo 10 11.4 4.3 5.1 <0.1

Example 4

The prepolymers 13 to 18 were prepared by mixing the ingredients ofprepolymer 3 of example 1 with DMDEE, DMEA, or secondary amine 1 asshown in Table 6. The free monomer content and the NCO value of theprepolymers were measured and compared with the free monomer content ofprepolymer 3. The formulations and results are listed in Table 6.

TABLE 6 Free NCO Secondary isocyante value in Prepo 3 DMDEE DMEA amine 1monomer prepo (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) Prepo 3 100.00.0 0.0 0.0 1.3 5 Prepo 13 99.9 0.1 0.0 0.0 1.1 5 Prepo 14 99.8 0.2 0.00.0 0.8 4.9 Prepo 15 99.7 0.5 0.0 0.0 0.5 4.7 Prepo 16 99.0 0.0 0.9 0.00.7 4.5 Prepo 17 98.2 0.0 1.8 0.0 0.3 4 Prepo 18 95.0 0.0 0.0 5.0 <0.14.1

It is to be understood that although preferred embodiments have beendiscussed for providing embodiments according to the present invention,various modifications or changes may be made without departing from thescope and spirit of this invention.

1. An isocyanate-containing prepolymer obtainable obtained by reactingat least one isocyanate with at least one first compound and with atleast one second compound different from said at least one firstcompound, both compounds being each independently selected from thegroup comprising monohydric alcohols, thiols and secondary amines; andwherein the at least one isocyanate comprises a methylene diphenyldiisocyanate.
 2. The prepolymer according to claim 1, wherein said atleast one second compound has a lower weight average molecular weightthan said at least one first compound.
 3. The prepolymer according toclaim 1, wherein said first compound is a monohydric alcohol selectedfrom the group comprising monohydric polyesters, monohydric C₁₋₂₀hydroxyalkyl, and monohydric heterocyclyl.
 4. The prepolymer accordingto claim 1, wherein said second compound is a monohydric alcoholselected from the group comprising monohydric polyesters, monohydricC₁₋₂₀ hydroxyalkyl, and monohydric heterocyclyl.
 5. The prepolymeraccording to claim 1, wherein said second compound comprises at leastone tertiary amine group.
 6. The prepolymer according to claim 1,wherein the ratio of the NCO value of the isocyanate-containingprepolymer, to the weighted average of the OH, SH or NH value, of saidfirst and second compounds ranges from 0.0005 to 1.0000.
 7. Theprepolymer according to claim 1, wherein said first compound is presentin a total amount of at least 40.0% by weight based on the total weightof the isocyanate-containing prepolymer.
 8. The prepolymer according toclaim 1, wherein said second compound is present in a total amount of atleast 0.001% by weight based on the total weight of theisocyanate-containing prepolymer.
 9. The prepolymer according to claim1, wherein the viscosity of the prepolymer ranges from 1000 to 200 000mPa·s, wherein the viscosity is measured at 25° C. using BrookfieldViscometer according to the ASTM D 4889 standard without any plasticizeradded to the prepolymer.
 10. The prepolymer according to claim 1,wherein the prepolymer has a free isocyanate monomer content of at most1.0 wt %, as measured by quantitative HPLC GC analysis.
 11. A processfor preparing an isocyanate-containing prepolymer as defined in claim 1,comprising the steps of: (a) reacting at least one isocyanate with atleast one first compound selected from the group comprising monohydricalcohols, thiols and secondary amines; and (b) reacting the at least oneisocyanate and/or the product of step (a) with at least one secondcompound selected from the group comprising monohydric alcohols, thiolsand secondary amines, wherein said second compound is different fromsaid first compound; thereby preparing an isocyanate-containingprepolymer.
 12. A polyisocyanate composition comprising the prepolymeras defined in claim
 1. 13. (canceled)
 14. An adhesive comprising theprepolymer as defined in claim
 1. 15. A one component self levelingliquid membrane prepared from a prepolymer as defined in claim
 1. 16.The adhesive according to claim 14, wherein the adhesive is a onecomponent adhesive.